Anti-induction telephone system.



W-OONDON & A. BARRETT. ANTI-INDUCTION TELEPHONE SYSTEM.

APPLICATION FILED MAY 27, 1907.

910, 177. Patented Jan. 19. 1909.

. 2 SHEETS-SHEET 1.

WlTNESSES.-' Qua/aw 11v VENTORS W. OONDON & A. BARRETT.

ANTI-INDUCTION TELEPHGNE SYSTEM.

APPLIOA'I'ION rum) my 27, 1901.

91 O, 1 77. Patented Jan. 19. 1909.

2 SHEETS-BKEET 2.

WITNESSES: A INVENTORS, ,j:t 2 tfiz w uam, 7340M =-Wm44 A TTORNE Y.

m: NORRIS PETERS co., wAsnmo-rou. n. c.

WILLIAM CONDON AND ALBERT BARRETT, OF KANSAS CITY, MISSOURI.

ANTI-INDUCTION TELEPHONE SYSTEM.

Specification of Letters Patent.

Application filed May 27, 1907.

Patented Jan. 19, 1909.

Serial No. 375,978.

To all whom it may concern:

Be it known that we, \VILLIAM GoNDoN and ALBERT BARRETT, citizens of the United States, residing at Kansas City, in the county of Jackson and State of Missouri, have invented certain new and useful Improvements in Anti Induction Telephone Systems, of which the following is a specification.

Our invention relates to an improved antiinduction telephone system.

Our invention is adapted particularly for telephone systems in which the transmitters and a battery are located in a primary line circuit, the receiver telephones being located in secondary circuits inductively related to the primary circuit.

The object of our invention is to provide a telephone system in which disturbances due to induction and set up in the primary circuit are eliminated from the secondary circuits.

Our invention provides a telephone system in which the disturbing currents traversing the primary circuit are employed to induce in the secondary receiving circuits currents contrary in direction but substantially equal in strength, and which therefore nullify each other. In the preferred form of our invention direct currents, such as are generated by a battery, are employed for the telephonic currents in the primary circuit. We have found that the telephonic currents induced in the secondary circuit, which circuit contains the receiving telephone, are much stronger than the currents induced in the secondary circuit by the disturbing currents in the primary circuit. Such disturbing currents in the primary circuit are usually alternating currents due to induction from foreign sources, such as electric light or power currents. WVe have found that by subjecting two portions of the receiving circuit to the opposite inductive action of the alternating disturbing and the direct telephonic currents which traverse the primary circuit, that, so far as the ear can detect, the disturbing currents may be made to neutralize each other in the secondary circuit, while at the same time the sounds caused in the receiver by the telephonic currents are very distinct. lVe have found by experience, however, that the opposite inductive action exerted by the telephonic and other currents upon the two portions of the secondary or receiving circuit may be so proportioned that the telephonic currents induced in the secondary circuit, by reason of the inductive action on one portion of the circuit being greater than the inductive action upon the other portion of the circuit, will produce in the receiver good talk of considerable volume and unaccompanied by any other sounds due to induction. We have obtained this result in very noisy circuits in which the ground was employed as part of the primary circuit.

We have found that if an ordinary condenser be connected in series in the primary transmitting circuit that the induced telephonic currents set up by the condenser will themselves have feeble inductive action upon another circuit compared with the inductive action of the original direct telephonic currents. On the other hand, we have found that the currents induced in the condenser by the disturbing alternating currents in duced in the primary circuit are capable of inducing in the secondary circuit currents very near equal in strength to the currents induced in the secondary circuit by the original disturbing currents.

By the employment of the principles just stated in the preferred form of our invention, we have obtained on avery noisy grounded circuit remarkably loud and clear talk with an entire absence of other sounds due to disturbing currents traversing the line.

Other novel features of our invention are hereinafter fully described and claimed.

In the accompanying drawings, we have illustrated different means for carrying our invention into effect.

Figure 1 is a diagrammatic view of a telephone system in which the primary circuit is divided into a plurality of pairs of branches, a pair of branches being located at each station, a condenser and a variable resistance device being located respectively in the two branches of each pair, two portions of the primary winding of an induction coil being located respectively in the two branches of each pair, the secondary winding of the induction coil being located in the secondary circuit which also includes the telephone receiver. Fig. 2 is a diagrammatic representation of a telephone system, similar to that shown in Fig. 1, with the oxception that the induction coil is dispensed with, but two portions of the secondary circuit are subjected to opposite inductive action by the two branches of the primary circuit. Fig. 3 is a diagrammatic representation of a telephone system employing another modified form of our invention. In this form the apparatus is similar to that shown in Fig. 1. The variable resistance devices in the branches being dispensed 'with, one portion of the primary winding of the induction coil being inductively related to the secondary winding to a greater extent than the other portion of the primary winding. In Fig. 4, which represents a telephone system for carrying into effect another modified form of our invention, the two branches of the primary circuit at each station, contain respectively a condenser and a transmitter and are connected at their ends to the ground and to opposite ends of the. primary winding of the induction coil, the line wire being connected centrally to theprimary winding of the induction coil. Fig; 5' represents a telephone system similar to that shown in Fig. 1, the condensers and variable resistance devices not being employed. Fig. 6 represents two forms of apparatus for carrying into effect two modified forms of our invention. In this figure the primary windings of the two induction coils, are located in series in. the primary or transmitting circuit. In the form shown at station A, the two portions of the primary winding are oppositely wound, the secondary winding at that station being all wound in the same direction. In the form shown at station B, the two portions of the secondary winding are oppositely wound, the primary wire being all wound in the same direction. Fig. 7 represents a telephone system similar to that shown in Fig. 1, the condensers however, being replaced by resistance coils. Fig. 8 is a view similar to Fig.1, with the exception that in Fig. 8 the resistance coils 9 and contacts 8 at stations A and Bv are omitted. Fig. 9 represents a central longitudinal sectional view of the induction coil shown in Figs. 1 and 1, and a diagrammatic representation of the other parts of the apparatus employed at a station.

Similar characters of reference denote similar parts.

Referring to Fig. 1, which illustrates one form of our invention, the primary circuit comprises a line conductor 1, which connects stations A and B, a battery 2, forming a portion of said conductor. The primary circuit at each station A and B, is divided into two branches united at opposite ends, the ground forming the return conductor. The apparatus at the two stations being identical, a description of one will sufiice. 3 denotes the primary winding of an induction coil, the opposite ends of which are connected respectively to two conductors 4 and 5, the conductor 1 being connected to one pole of a condenser 6, the opposite pole of which connected to conductor 1.

connects to a conductor 7, which is connected to the conductor 1. The. conductor 5 is connected to the movable contactS, adapted to bear consecutively on the coils of a resistance coil 9, which has one end connected to a conductor 10, which in turn is The contact 8 and coil 9 form an ordinary variable resist ance device. 11 denotes an ordinary telephone transmitter located in and forming a part of a conductor 12, one end of which is connected to the ground, the other end being connected to the central whirl of the primary winding 3. 13 denotes the secondary winding of the induction coil, opposite ends of which are connected respectively to two conductors 1A, which in turn are connected respectively to the opposite poles of an ordinary telephone receiver '15. One branch of each pair of branches comprises conductors t and 7, condenser 6, and one half of the primary winding 3. The other branch comprises the other half of the primary winding 3, conductors 5 and 10, and the variable resistance device 8-9. 16 denotes a foreign circuit adjacent to the primary circuit and from which are induced the disturbing currents which traverse the primary circuit. 17 denotes the core of the induction coil, preferably comprising a bundle of small iron wires that portion lying within the portion of the primary winding which is located in the branch containing the condenser 6, containing preferabl for the reason hereinafter 'iven 100 eration of the system illustrated in Fig. 105

1 :The telephonic and disturbing currents passing along the conductor 1 will divide at stations A and B, the direct battery telephonic currents and a portion of the induced disturbing currents will pass by means of 110 conductors 10 and 5 and variable resistance device 89, into and through one portion of the primary winding 3, and thence by conductor 12 and transmitter 11 to ground.

The direct and alternating disturbing cur- 115 rents will also pass into the conductor 7 of the other branch, and by means of a condenser 6, will induce alternatingcurrents in a conductor i, which will pass through the other portion of the primary winding and 120 thence through conductor 12 and transmitter 1.1, to, ground. Both portions of the primary winding 3 being wound in the same direction, and the induced and direct currents from the branches passing in opposite 12 5 directions'through the two portions of the primary winding, will induce currents opposite in direction in the secondary winding 13. The currents induced in the branch containing the condenser 6- by the original dis-.130

turbing currents will not have the same inductive effect upon the secondary winding 13 as will have the original disturbing currents which pass through the branch containing the conductor 10. The result would be therefore, that the original disturbing currents passing through that portion of the primary winding located in the branch containing the conductor 5, will, unless it is otherwise prevented, exert a preponderating inductive influence upon the secondary winding 13 and currents would flow in the secondary circuit which would cause disturbing noises in the telephone receiver 15. The inductive influence of the original disturbing currents and the inductive influence of the currents induced in the other branch thereby may be equalized or balanced in different ways. One way to balance or equalize the two fields of induction formed between the primary and secondary windings by the original and the induced disturbing currents is to reduce the inductive efiiciency between that portion of the primary winding 3, located in the branch containing the conductor 5, and the secondary winding 13. This reduction in efficiency may be obtained by having the portion of the core 17, which is located in that portion of the primary winding, contain less iron than the other portion of the said core. Figs. 1 and 4 show such a core. Another way for balancing or equalizing the two inductive fields caused by the disturbing currents, is illustrated in Fig. 3. In this form the core throughout is of equal diameter, but a greaer length of the primary winding is located in the branch containing the condenser 6, the conductor 12 being connected to the primary winding at one side of the central portion thereof. Another plan for equalizing or balancing the two opposite inductive fields is by the insertion of a proper amount of resistance in the branches containing the conductors 10, such resistance being the resistance devices S t), shown in Figs. 1 and 7. Another means for balancing the inductive fields is by movement of the core 17 lengthwise to the proper position. The two opposite fields of induction set up by the opposing original and induced disturbing currents being balanced or equalized, the currents induced in the secondary circuit will be in the contrary direction and of equal strength and will therefore nullify each other, so that none of the disturbing sounds will be heard in the telephone receiver located in the secondary circuit. The currents induced in the branch containing the condenser 6, by the direct telephonic currents traversing the primary, will have feeble effect in their inductive action upon the secondary winding 13 as compared with the powerful efiect of the direct telephonic currents traversing the branch containing the conductor 5. The currents set up in the secondary circuit by the telephonic currents induced in the branch containing the condenser 6, will be comparatively weak and will not reduce to any appreciable extent the currents induced in the secondary circuit by the direct telephonic currents. The result will be that the telephonic sounds produced in the receiver will be very loud and distinct and disturbing sounds due to induction will be wholly eliminated.

In the form shown in Fig. 2 the apparatus employed is the same as in Fig. 1 with the exception that the induction coil is eliminated. Referring to the said Fig. 2, 13 denotes a portion of the secondary circuit comprising a conductor disposed parallel with. a conductor 3, said two conductors be ing inductively related to each other. The conductor 13 has its ends connected respectively to conductors 14, which are connected to the opposite poles of the telephone receiver 15, and constitute, with said receiver and conductor 13 the secondary circuit. The conductor 3' has its ends connected respectively to the conductors 1 and 5 which in turn are connected respectively to the condenser 6 and contact point 8. The conductors 7 and 10 are connected respectively to the condenser 6 and resistance coil 9 and also at their other ends to the conductor 1. The conductor 12, similar to that shown in Fig. 1, is connected midway between the ends of the conductor 13 to the conductor 3.

In the form shown in Fig. 2 the divided currents passing over the two branches of the primary circuit set up fields of induction of opposite character betweenthe sec ondary conductor 13 and the two portions of the conductors 3, disposed upon opposite sides of the conductor 12. By adjusting the variable resistance 89 the two fields of illdu'ction formed by the disturbing currents may be equalized. The direct telephonic currents passing through the branch comprising the conductors 5 and 10, resistance device 8-9 and the portion of the conductor 3 to the left of the conductor 12, will induce much stronger telephonic currents in the secondary circuit than are induced in said circuit by the induced telephonic currents traversing the opposite branch containing the condenser 65, and the talk heard in the telephone receiver will be loud and clear and free from disturbing sounds due to induction.

The form shown in Fig. 5 is similar to that shown in Fig. 1 with the exception that the variable resistance device is omitted and the conductor 10 connects directly with the conductor The conductor 12, as stated hereinbefore, connects to the primary winding 3 at a point nearer one end than the other, so that the inductive fields set up by the original and the induced disturbing ourrents passing through the two branches respectively, will be balanced or equalized, as has been already described.

In the form shown in Fig. 4 the secondary circuit is identical with that shown in Fig. 3. In this form the conductor 5 connects with the central portion of the primary winding of the induction coil, one end of which is connected to the conductor 12, which contains the transmitter 11 and is connected with the ground. The other end of the primary winding is conneced to the conductor 17 which is connected to one pole of a condenser 6, the other pole of which is connected to a conductor 18, which is connected with the ground.

In the form of the invention shown in Fig. 1, the direct telephonic and the alternating disturbing currents pass from the conductor 1 over the conductors 10 and 5, dividing at the center of the primary winding of the induction coil, the direct telephonic current passing through that portion of the primary winding connected to the conductor 12, thence by said conductor 12 to the ground. The disturbing currents and the direct telephonic currents fill that portion of the primary winding connected with the conductor 17, causing alternating currents to be induced by means of the condenser 6 and the conductor 18. As described with reference to the preceding forms, two opposite fields of induction are formed between the primary and secondary windings which generate opposite currents in the secondary circuit. To balance the inductive fields produced by the disturbing currents, a core 17, similar to that shown in Fig. 1, is provided in the induction coil, the smaller portion being located in that portion of the primary winding through which the circuit tele phonic currents pass.

The form shown in Fig. 5 is similar in construction to that shown in Fig. 3, with the exception that the condenser 6 is omitted and the conductor 12 connects centrally with the primary winding of the induction coil. The condenser being omitted and the inductive fields being similar and equally balanced, the telephonic and disturbing currents would pass equally through both branches of the primary circuit and the currents set up in the secondary winding would be equal and contrary in direction, and no sounds would be heard in the receiver 15. By lengthwise moving the primary winding 3 and core 17 relative to the secondary winding 13, the two fields of induction may be so unbalanced that the telephonic currents passing through one branch will have more effect on the secondary circuit than will those passing through the other branch. o have found by actual test that such adjustment may be made so that very good clear talk may be heard in the receiver before any disturbing sounds due to induction will manifest themselves. The field may be similarly unbalanced by wlthdrawlng the core 17 from the primary winding, the

distance said core is withdrawn being determined by trial. That is, it may be withdrawn until the disturbing sounds are faintly heard, at which time the telephonic sounds will be quite loud and very clear.

In Fig. 6 an apparatus is shown which illustrates two modifications. The secondary circuit at station A corresponds to the secondary circuit shown in Fig. 1. The primary winding 3 of the induction coil at station A comprises two equal portions wound around the core 17 in opposite directions, said primary winding preferably extending at its ends beyond the ends of the secondary winding 13. The line conductor 1 has its ends connecting respectively to one set of ends of the primary windings 3 and 3 the other ends of said primary windings being connected respectively to the two conductors 12, which extend to the ground and include the transmitters 11. The secondary winding l3 at station B, has two portions oppositelywound, the ends of the secondary winding preferably extending beyond the ends of the primary winding 3 which encircles a core-17. The two cores 17 are each of equal diameter throughout. The telephonic and disturbing alternating currents passing over the conductor 1, will pass through the primary windings 3 and 3 If the two portions of the primary winding 3 have exactly the same number of convolutions exposed to the same number of convolutions in the secondary winding 13, and are otherwise related in exactly the same way to the secondary winding, the two opposite fields of induction set up by the currents passing through the oppositely wound'portions of the primary winding 3, will be of the same strength and the currents produced in the secondary circuit at station A would neutralize each other. By moving either of the two windings, 3 or 13, lengthwise rela tive to the other winding, the two fields of induction may be changed so that one will preponderate over the other. The telephonic currents induced in the secondary winding 13 being the stronger will be the first to cause sound to be heard in the receiver 15, at station A. The more the fields of induction at station A are relatively changed the louder the telephonic sounds that will be heard in the receiver at that station. This adjustment may be continued until the fields of induction are so unbalanced that the disturbing sounds by induction may be faintly heard in the receiver. It will be found that before this occurs the telephonic sounds will be quite loud and very distinct. At station B the currents passing through the primary winding 3 will, owing to the secondary winding being oppositely wound in its two portions, induce currents of equal strength and contrary in direction in the secondary circuit at station B. The two fields of induction at station B may be unbalanced to a degree that telephonic sounds but not the disturbing sounds will be heard in the receiver 15 at station B. This unbalancing of the two fields of induction may be obtained as described with reference to the apparatus at station A, by a movement lengthwise of one of the two windings of the induction coil relative to the other. The two fields of induction at either station A or station 13 may also be unbalanced to the proper degree by lengthwise movement in the primary windings of the cores 17.

Fig. 7 represents a modified form of telephone system similar to that shown in Fig. 5 excepting that each branch at each station contains a resistance device. The conductor 7 is connected to one end of a resistance coil, the other end of which connects to the conductor a which also connects with one end of the primary winding In the opposite branch the conductor 10 connects with the movable contact 8 which bears upon the resistance coil 9, said resistance coil connecting at one end to the conductor 5 which connects with the other end of the primary winding 3. The conductors 12 at each station connect to the central portion of the primary winding and also with the ground.

In the form shown in Fig. 7 the telephonic and disturbing currents divide and pass at each station through the two branches containing the resistances 18 and 8-9. By properly moving the contact 8 the opposite magnetic fields established between the two portions of the primary winding 3 and the secondary winding 13, may be unbalanced to a degree in which telephonic but not the disturbing sounds will be produced in the receivers 15. Adjustment of the contact 8 to a position in which either more or less resistance will be in one branch than in the other branch will effect this result. The proper posit-ion for the contact 8 may be det rmined by experiment.

In Fig. 8 is illustrated the preferred apparatus for carrying into effect the preferred form of our invention. This form of apparatus is similar to that shown in Fig. 1 with the exception that the variable resistances S-9 are dispensed with, the conductors 10, which are connected to the conductor 1, being connected to the conductors 5 respectively, which in turn are connected respectively to one set of ends of the primary windings 3 of two induction coils, located respectively at stations A and 13. Two conductors 12, including therein respectively the transmitters 11, connect at one set of ends at the two stations A and B, to

the ground, the other set of ends being connected respectively to the central portions of the primary windings 3 respectively. Two cores 17 are inserted in the primary windings 3 respectively, that portion of each core located in that portion of the primary winding 3 which is located in the branch containing the conductors 5 and 10, having less diameter than the other portion of the core. The conductors 7, which connect at stations A and B respectively with the conductor 1, are connected respectively to like poles of the two condensers G, the opposite poles of which are connected respectively to the conductors 4, which in turn connect respectively with the ends of the primary windings 3, opposite those to which are connected the conductors 5. The conductor 1 includes a battery 2. The ends of the secondary winding 13 are connected respectively to conductors 14L which connect with the two bind ing posts of the telephone receiver15.

In the preferred form of apparatus shown in Fig. 8, the direct telephonic and the alternating disturbing currents pass through conductor 1, thence through conductors 10 and 5, thence through one portion of the primary winding 3 to conductor 12, and thence to ground. The said direct and alternating currents passing over conductor 7 induce currents by means of the condenser G. Said currmts being alternating in form, pass through conductor 4:, thence through the adjacent portion of the primary winding 3, to the conductor 12, and thence to ground. As hercinbeforc stated, the direct telephonic currents and the original disturbing currents which pass through the branch containing the conductor 5, have greater inductive efiect upon the secondary winding 13 than the currents induced by means of the condenser G. In order that the two opposite fields of induction, which are produced by the original disturbing currents passing through one branch and by the induced alternating disturbing currents passing through the opposite branch, may be balanced, the inductive efiiciency between the secondary winding 13 and that portion of the primary winding through which passes the direct telephonic currents must be less than the inductive cfliciency between the other portion of the primary winding and the secondary winding. As illustrated in Fig. 8 this may be obtained by providing a core having a larger amount of iron in that portion of the primary winding connected with the condenser G by the conductor 4.. Or the fields of induction may be unbalanced to the proper degree by longitudinal movement of the core 17 in the primary winding or by longitudinal movement of one of the windings of the induction coil relative to the other.

I11 Fig. 9 is illustrated in central longitudinal section an induction coil of the type employed in the forms shown in Figs. 1, t, and 8. In this figure is illustrated a spool 19, which contains a series of layers of wire which forms the secondary winding 13.

, mary winding 3.

One end of the winding 18 is connected to one of the conductors 14, which at its opposite end is secured to one of the binding posts of the telephone receiver 15. The other end of the winding 13 is connected by a conductor 14 to the opposite binding post. Located in the axial hole in the spool 19 is a spool 20', on the periphery of which are wound two coils of wire which form the pri- The two coils of wire are in one or more layers and are of equal length. These two coils of wire are wound in the same direction and have their inside ends connected to each other by a conductor 21. The opposite ends of the two coils are connected respectively to the two conductors 4 and 5, which connect respectively to one pole of the condenser 6 and to the conductor 10. The core 17 comp "ises preferably a plurality of small wires located within the central opening of the spool 20. That portion of the core which is embraced by the coil or" wire connected to the conductor 4, preferably contains a greater number of soft iron wires than is contained in that portion embraced by the coil which connects with the conductor 5.

v Vhile the drawings illustrate the ground as forming a part of the primary circuit, it will be obvious that a metallic conductor may be employed for the return portion of the circuit. In employing the ground for the return portion of the circuit results equally as good as with a metallic return are obtained, so that by dispensing with the metallic return much expense of construction may be obviated. In the employment of a ground connection for the line conduct-or those static discharges which frequently occur in metallic circuits are obviated.

lflany modifications other than those shown and described may be made within the scope of the appended claims without departing from the spirit of our invention.

Having thus described our invention, what we claim and desire to secure by Letters Patent is 1. In a telephone system, the combination with a primary circuit, of a secondary circuit having two portions oppositely induct' ively related to the primary circuit, one of said portions having relative to the primary circuit an inductive field of greater etficiency than the inductive field between the other of said two portions and the primary circuit.

2. In a telephone system, the combination with a primary circuit, of a plurality of secondary circuits each having two portions oppositely inductively related to the primary circuit, one of each of said portions having relative to the primary circuit an inductive field of greater efiiciency thanthe other of said portions.

In a telephone system, the combination with a primary circuit, of means for generating telephonic currents in said circuit, a secondary circuit, a telephone receiver in said secondary circuit, an induction coil having its primary and secondary windings located respectively in said primary" and secondary circuits, one of said windings having two portions oppositely inductively related to the other winding, the inductive efliciency between one of said portions and the other winding being greater than the inductive efiiciency between the other portion and said other winding.

4. In a telephone system, the combination with a primary circuit, of means for generating telephonic currents in said circuit, a plurality of secondary circuits, a plurality of telephone receivers located one in each of said secondary circuits, a plurality of in duction coils each having its primary and secondary windings located respectively in said primary and one of said secondary circuits, one of the windings of each induction coil having two portions oppositely inductively related to the other winding of said coil, the inductive etficiency between one of said portions and the other winding of said coil being greater than the inductive efliciency between the other port-ions and said other winding. p

5. In a telephone system, the combination with a primary circuit having two branches, of means torgenerating telephonic currents in said circuit, a secondary circuit, a telephone receiver in said secondary circuit, and an induction coil having its secondary winding located in the secondary circuit, its primary winding having two portions located respectively in said two branches, said two portions being oppositely inductively related to the other winding, the inductive efiiciency between said two portions and the other winding being different.

6. In a telephone system, the combination with a primary circuit having two branches, of means for generating telephonic currents in said circuit, a secondary circuit, a telephone receiver in said secondary circuit, a condenser located in one of said branches, and an induction coil having its primary and secondary windings located respectively in said primary and secondary circuits, one of said windings having two portions oppositely inductively related to the other winding, said two portions being located re spectively in said two branches.

7. In a telephone system, the combination with a primary circuit having two branches, of means for generating telephonic currents in said circuit, a secondary circuit, a telephone receiver in said secondary circuit, a condenser in one of said branches, and an induction coil having its secondary winding located in the secondary circuit and havin two portions of its primary winding locate respectively in said two branches, said two portions being oppositely inductively related to the other winding, and the inductive efficiency between one of said portions and the other Winding being greater than the inductive efiiciency between the other portion and said other winding.

8. In a telephone system, the combination with a primary circuit having two branches, of means for generating telephonic currents in said circuit, a secondary circuit having two portions oppositely inductively related to said two branches respectively, there be ing greater inductive efficiency between one portion of the secondary circuit and the ad jacent branch than between the other portion of the secondary circuit and the other branch, and a telephone receiver in said secondary circuit.

9. In a telephone system, the combination with a primary circuit having two branches, of means for generating telephonic currents in said circuit, a condenser located in one of said branches, a secondary circuit having two portions oppositely inductively related to said two branches respectively, and a telephone receiver in said secondary circuit.

10. In a telephone system, the combination with a primary circuit having two branches, of means for generating telephonic currents in said circuit, a condenser located in one of said branches, a secondary circuit having two portions oppositely inductively related to said two branches respectively, the inductive efliciency being greater between one of said portions and the adjacent branch than between the other of said portions and the other branch, and a telephone receiver in said secondary circuit.

11. In a telephone system, the combination with a primary circuit having two branches, of means for generating telephonic currents in said circuit, a resistance device located in one of said branches, a secondary circuit having two portions oppositely inductively related to said two branches respectively, and a telephone receiver located in said secondary circuit. I

12. In a telephone system, the combination with a primary circuit having two branches, of means for generating telephonic currents in said circuit, a condenser located in one of said branches, a resistance device located in the other of said branches, a secondary circuit having two portions oppositely inductively related to said two branches respectively, and a telephone receiver in said secondary circuit.

13. In a telephone system, the combination with a primary circuit having two branches, of means for generating telephonic currents in said circuit, a condenser located in one of said branches,- a secondary circuit, a telephone receiver located in said secondary circuit, and an induction coil having its secondary winding located in said secondary circuit and having two portions of its primary winding located respectively in said two branches, said two portions being oppositely inductively related to the secondary winding of said coil.

14. In a telephone system, the combination with a primary circuit having two branches, of means for generating telephonic currents in said circuit, a condenser located in one of said branches, a secondary circuit, a telephone receiver located in said secondary circuit, and an induction coil having its secondary winding located in said secondary circuit and having two portions of its primary winding located respectively in said two branches, said portions being oppositely inductively related to the other winding and having different inductive efficiency relative to the other winding.

15. In a telephone system, the combination with a primary circuit having two branches, of means for generating telephonic currents in said circuit, of a condenser located in one of said branches, a resistance device located in the other of said branches, at secondary circuit, a telephone receiver in said secondary circuit, and an induction coil having its secondary winding located in said secondary circuit and having two portions of its primary winding located respectively in said two branches, said two portions being oppositely inductively related to the second ary winding.

16. In a telephone system, the combination with a primary circuit having a plurality of pairs of branches, of means for generating telephonic currents in said circuit, a plurality of secondary circuits, a plurality of of said secondary circuits, and a plurality of induction coils each having its secondary winding located respectively in said second ary circuits and each having two portions oppositely inductively related to the secondary winding and located respectively in a pair of branches, the inductive efficiency between each of said two portions and the adjacent secondary winding being diflierent.

17 In a telephone system, the combination with a primary circuit having a plurality of pairs of branches, of means for generating telephonic currents in said circuit, a plurality of secondary circuits, telephone receivers located one in each of. said secondary circuits, a plurality of condensers located one in a branch of each pair, and a plurality of induction coils each having its secondary winding located in one of said secondary circuits, the primary winding of each induction coil having two portions oppositely inductively related to the secondary winding telephone receivers located one in each' and located respectively in the two branches of one 01"? said pairs.

18. In a telephone system, the combination with a primary circuit having a plurality of pairs of branches, of means for generating telephonic currents in said circuit, a plurality of secondary circuits each having two portions oppositely inductively related to the branches respectively of one of said pairs, one portion of each of said secondary circuits having greater inductive efliciency than the other portion relative to the adjacent branch, and a plurality of telephone receivers located respectively in said secondary circuits.

19. In a telephone system, the combina tion with a primary circuit havinga plurality of pairs of branches, of means for generating telephonic currents in said circuit, a plurality of condensers located one in a branch of each pair, a plurality of secondary circuits each having two portions oppositely inductively related to the branches respectively of a pair, and a plurality of telephone receivers located one in each of said secondary circuits.

20. In a telephone system, the combination with a primary circuit having a. plurality of pairs or" branches, of means for generating telephonic currents in said circuit, a plurality of condensers located one in a branch of each pair, a plurality of secondary circuits each having two portions oppositely inductively related to two branches of a pair, the inductive efficiency between one of said portions and the adjacent branch being greater than between the other of said portions and the other branch, and a plurality of telephone receivers located respectively one in each of said secondary circuits.

21. In a telephone system, the combination with a primary circuit having a plurality of pairs of branches, of means for generating telephonic currents in said circuit, a plurality of resistance devices located one in the branch of each pair, a plurality of secondary circuits each having two portions oppositely inductively related to a pair of branches, and a plurality of telephone receivers located one in each of said secondary circuits.

22. In a telephone system, the combination with a primary circuit having a plurality of pairs of branches, of means for generating telephonic currents in said circuit, a plurality of condensers located one in a branch of each pair, a plurality of resistance devices located respectively in the other branches of said pairs, a plurality of secondary circuits each having two portions oppositely inductively related to a pair of branches respectively, and a plurality of telephone receivers located in said secondary circuits respectively.

23. In a telephone system, the combinaportions of its primary winding located respectively in a pair of said branches, said two portions being oppositely inductively related to the secondary winding of the coil.

24:. In a telephone system, the combination with a primary circuit having a plurality of pairs of branches, of means for generating telephonic currents in said circuit, a plurality of condensers located one in a branch of each pair, a plurality of secondary circuits, a plurality of telephone receivers located respectively in said secondary circuits, and a plurality of induction coils each having its secondary winding located in one of said secondary circuits, and having each two portions of its primary winding located respectively in a pair of branches, said two portions being oppositely inductively related to the secondary winding and having diiterent inductive efiiciency relative to said secondary winding.

25. In a telephone system, the combina tion with a primary circuit, of means for generating a direct current in said circuit, a transmitter in said circuit, a secondary circuit having two portions oppositely inductively related to said primary circuit and a receiver in said secondary circuit.

26. In a telephone system, the combination with a primary circuit having two branches, of means for generating a direct current in said circuit, a transmitter in said circuit, a condenser in one of said branches, a secondary circuit, a receiver in said secondary circuit, and an induction coil having its secondary winding in said secondary circuit and having two portions of its primary winding located respectively in said two branches.

27. In a telephone system, the combination with a primary circuit having two branches, of means for generating in said circuit a direct current, a transmitter in said circuit, a condenser in one of said branches, a secondary circuit having two portions oppositely inductively related to said branches respectively, and a receiver in said secondary circuit.

28. In a telephone system, the combination with a primary circuit having two branches, of means for generating a direct current in said circuit, a transmitter in said circuit, a condenser in one of said branches, a secondary circuit having two portions oppositely and unequally related inductively to said branches respectively, and a receiver in said secondary circuit.

29. In a telephone system, the combination with a primary circuit having two branches, of means for generating a direct current in said circuit, a transmitter in said circuit, a condenser in one of said branches, a secondary circuit, a receiver in said secondary circuit, and an induction coil having its secondary winding in said secondary circuit, and having its primary winding composed of two portions located respectively in said two branches and oppositely and unequally inductively related respectively to said secondary winding.

In testimony whereof we have signed our names to this specification in presence of two subscribing witnesses.

WILLIAM CONDON. ALBERT BARRETT.

Witnesses:

WARREN D. HOUSE, E. B. HOUSE. 

